


The Other Threesome

by morefishplease



Series: Comfy Fish Stories [69]
Category: Undertale (Video Game)
Genre: Creampie, Multi, POV First Person, Threesome - F/M/M
Language: English
Status: Completed
Published: 2018-01-22
Updated: 2018-01-22
Packaged: 2019-03-08 04:32:36
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,858
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13450620
Author URL: https://archiveofourown.org/users/morefishplease/pseuds/morefishplease
Summary: You and Mettaton give Undyne a threesome for her birthday.





	The Other Threesome

I wake up when he pushes the door open, but I stay very still and quiet, pretending to sleep. I thought what I’d do was surprise him when he crawled into bed next to me, just sort of pounce on him and kiss him all over. He gets startled very easily, I’ve noticed, his eyes get very wide and he puts his hands up and he jumps like a foot but I think it’s cute. He’s very cute in general, you know. I always thought I’d end up falling for someone big and tough and macho, someone who could throw me around, but I’ve managed to surprise myself. I think I like knowing that I’m in complete control at all times, that if I wanted to I could kill him, or I could take his clothes off and make him hard and do whatever I liked with him and he wouldn’t be able to stop me. I don’t think I’d dare to, I’d get too flustered and he’d probably never trust me again. Unless it turned him on, which is a possibility. Either way I’m not going to, it’s not worth it. Probably not worth it. Sometimes when he’s not around I think about it when I masturbate. It’s funny that that’s changed too, ever since he’s entered the picture. It used to be I’d think about Alphys, or Brill, or I’d go and watch lesbian porn or something. Now I just think about him. He’s just so he’s so lean and small and

Cute isn’t the right word but I keep wanting to use it. He isn’t cute, necessarily, unless he’s trying to be. He has this sort of pointy face, very handsome of course, and these small little shoulders that I want to just take in my hands and knead and kiss and a cute flat stomach

I’ve used it again, I got ahead of myself. I don’t know the right word for it. He’d know, ironically enough, he’d know the perfect word. Maybe I’ll ask him later only try and make sure he doesn’t figure out why I’m asking. So if that part is whited out, dear whoever is reading my diary, you’ll know that I figured it out. Before I come kill you, of course. Stop now, you’ve been warned.

I’m rambling because I’m trying to stall. I’m afraid I’m going to get too flustered and turned on while I’m writing this down and I can’t, I literally can’t go again, if I try and touch myself I’ll die. I’m so sore and tired and bruised but I’m getting wet just thinking about it. I can’t win. I want to write it all down so I’ll remember all of the details but I know I’m just going to end up getting horny. I

I got up and put on looser clothes. So I can put my hand down my pants while I’m writing, or I can slip my hand up my shirt or whatever. I’m trying very hard to focus. I must not get flustered. I have to remember all this.

I lie there and pretend to be asleep and the whole time I’m starting to get this idiot grin on my face cause I’m like anticipating scaring him and wrapping him up in my arms and kissing him. I’m blushing just writing this, I’m a total dork. I lie there and feel two people get up on the bed, one on either side of me, and I just sort of freeze and like a bolt of lightning went through me and I thought ‘oh shit, I’m going to die,’ and so I fling the covers off and get ready to fight but it’s him and Mettaton, both in their underwear. I’d never seen Mettaton naked, or almost naked before, so I sort of stared at him. I was trying not to since my boyfriend was right there, obviously, but I couldn’t help myself. Mettaton is so slim and pretty. You’d think that maybe he’d look worse without his clothes on, since he’s a robot, obviously, but he actually looks really good, the metal plates all sort of come together in the center of his chest and strike down toward his groin. I remember the first time I met him I actually thought he was a girl, just like one of those really skinny narrow-hipped girls. I actually flirted with him for a little bit before I found out he was a guy, and then I stopped. I was too mortified because I thought he knew I thought he was a girl, but I never asked him or anything. I think it’s far enough in the past that I can laugh about it now but I still get a little embarrassed when I think about it.

I felt myself getting really standoffish because I didn’t know what was going on, so I sort of shrunk back and pulled the covers up and waited for them to talk. My boyfriend asked me if I remembered his birthday present and then it all sort of clicked together for me and I started smiling and

A lot of the time I’m not the sort of hyperaggressive confident Undyne that I think people see me as. When I’m alone I’m very calm and quiet and collected. It’s only when I’m around people I don’t know that I sort of slip into it. Ever since I was a kid that’s what I’ve done. I

I’m not going to psychoanalyze myself, there’s no point. I’m getting distracted again, or I’m trying to distract myself. From now on I’ll get right to the point. Although what I was trying to say is that I’m not always like that but that moment I realized what they were up to I felt my pupils dilate like they always do when I’m getting into that zone and I felt myself grinning. It was kind of like I was riding on my shoulders watching rather than being in control of everything. I was tingling a little bit, like in my hands and legs and in my crotch.

So I told them I got it already and to come here and they sort of laid up next to and on top of me a little bit and we got all entangled and we made out for a while. Mettaton was very quiet, surprisingly, and I sort of wondered how my boyfriend roped him into this. Not that I was complaining, though. I took his head in my hands and he looked up at me and called me darling~ and I don’t know how he does it but he always gets the little squiggle after he says anything. He has such a nice voice, nice and rich and kind of stuck-up, I guess, but I don’t mind it. I kissed him, ran my tongue over his teeth. “Darling~” he says again, “who taught you to kiss so well?” and I sort of blushed because we both knew who it had to have been but I didn’t want to say her name, not right then. Then we

 

▪ ▪ ▪

 

Here Undyne pauses for a solid minute, her diary lying ignored on her stomach, fiddling with her pen, flipping it around in her fingers. She’s thinking about it, of course. How could she not think about it? It’s all there’s been to think about for the past day or so. She hadn’t been able to focus (or function) at work cause randomly she’d remember Mettaton’s cold metal lips kissing her neck or you pressing into her further and deeper than before, forcing another little moan out of her mouth and she’d feel herself getting wet or feel her nipples pressing against the harsh fabric of her dress shirt and she’d have to excuse herself again, go to the bathroom again, grip the sink with a tight-taloned grasp, crack the porcelain, calm down.

Undyne lies there, frowning to herself, and then looks down at her diary. It’s very girly; pink cover, floral pattern, sticker on the back proclaiming it to be on sale for 25 cents. A steal, Undyne had thought. She feels faintly revolted every time she looks at it but once she opens it, lets the blank white pages subsume her, it passes. She reaches down, takes the diary, rips the page that she’d been working on out, throws it toward the trash can. She misses and the balled-up paper plunks to the floor an inch away. “Fuck it,” Undyne says, tosses the pen to the side, puts her diary on the floor. She stares at the ceiling for a moment then reaches a hand up her shirt, cups her breast, flicks her stiffening nipple. She smiles in spite of herself; she’s thinking about it.

 

▪ ▪ ▪

 

As soon as she realizes what’s going on it’s like a switch flicked somewhere in her head; her grin widens and her eyes grow very wide and hungry. The pool of black ink slips over them again and somewhere deep inside there’s a light, that’s all. Otherwise they’re empty. You can see yourself reflected in them. Mettaton glances over at you, starts to say something, but Undyne reaches forward, hauls you both forward, She nuzzles at you hungrily, eyes flicking over to Mettaton, drinking in his lithe body. “What a good idea you had,” she purrs, and you gulp, not sure what will happen next. It starts slower than you had anticipated. Undyne gathers you both into herself, kisses you deeply, alternates her attention between you and Mettaton. While you kiss at her nipple eagerly he is kissing his way down her taut stomach, Undyne’s eyes flashing lustfully, watching him go down and down and down until his lips are poised just on the edge of her panties. He takes them in his mouth, slides them down, and Undyne’s grin widens as the smell of her arousal seeps out. You can feel yourself getting hard already, you’re prodding against her thigh and she wiggles it back and forth, batting your hardon with it. She lets out a deep breath as Mettaton sets his tongue against her clit and it is just like she is there again -

 

▪ ▪ ▪

 

I’ll have to pace myself I think and I reach down, take his pointed chin in my hand, cut to my boyfriend with my eyes. “Kiss him,” I whisper, and Mettaton starts to shake his head but I tighten my grip a little and he rolls his eyes, takes my boyfriend’s cheek his hand, kisses him deep and long and I let out a little breath. They break apart and my boyfriend giggles, that dork, he actually giggles and Mettaton laughs and ruffles his hair, calls him darling~ and even though it’s stupid I feel a little pang of jealousy in my stomach. Mettaton looks over and laughs, and I realize I let out a little growl and i must be going feral or something, I can feel it like a radiator inside me, these waves of arousal pressing outward from somewhere deep in my abdomen, and while I’m touching myself watching them make out I notice I’m thrusting my hips forward against my hand. I hadn’t even noticed I was so turned on and distracted, so I clap my hands, tell them that’s enough, make them stand up, take their underwear off. Mettaton is completely bare and I raise my eyebrow at him and a panel opens up and his cock pops out already hard and I can’t help myself, I take it into my mouth and it’s so warm and slick and ready for me that I can’t stand it I want it all now, and I’m jerking my boyfriend off while I take Mettaton in as far as I can, coughing a little against him, and I shake my head, let them stare at me as I squeeze my breasts, as I spread my legs and touch myself. I am so wet that I’m dripping on the floor, a long thin strand of fluid hanging from my clit, and I turn around, wiggle my ass at them and I can feel them pressing at me and my boyfriend spanks my ass, presses against me there and I start to stand up but Mettaton is under me and I can feel his cock get bigger and thicker and my eyes bulge and I start to say something but he reaches up, sticks two fingers in my mouth, shushes me, tells me it’s okay, darling, just try not to think too much~ and I give him a weak little nod and then my boyfriend is in me, pressing forward slowly, and it is so tight and then Mettaton surges forward, grabs my hips and presses me down onto him and it’s like I’ve fallen on a spear it just goes in and in and in and in and I scream, and they stop but I tell them to keep going, a little shaky I guess and they thrust into me, first gingerly then faster and faster and I can feel their cocks prodding at each other through the thin wall of tissue inside me somewhere, I can feel them nudging at each other, pressing against that wall, pushing back and forth and ‘oh god’ I think ‘they’re going to tear me’ I think it just sort of bubbles up in the middle of my head and the sheer sense of fullness down there is almost too much for me to bear. I almost come, almost, but I don’t want to yet, cause once I do I won’t stop until I force them off and away from me and I don’t want to, the feeling of them prodding at each other through that thin thin wall is so indescribable and I can’t let it stop I’d kill for it to go on forever and ever god they’re going to tear me what a delicious thought I’m making noises stupid noises I can’t control myself it feels too good, I can’t even see properly there’s spots dancing in my eyes and my breath is coming in a stupid little gasp and I’m blushing so hard my cheeks might burst but they’re starting to go faster and I can’t think and I can’t stop myself and they push me over the edge, there inside me, and I tighten down on them, feel them strain inside me and I oh god oh god oh god is my frenzied litany that I murmur

and they thrust

and I call out

and I twitch and writhe and come again and again and again and again and I can feel them twitch inside me and surge forward like a flood of warmth and my stupid brain is too burnt out to realize it for a moment but they’re coming inside me and I can feel it everywhere, so deep it feels like it must be in my stomach and I can feel their cocks pulsing as they jet out into me and it makes me twitch and come again and by now my ribs hurt and there is a pain beneath my heart and I have to stop, they have to stop and they finally do and I can slow down and breathe

just breathe

for a moment

in gasps

and halting

breaths

in

and out

and then they pull out of me and everything starts to seep out and I feel myself blushing because it must be disgusting it must be it has to be but why does it turn me on so much, why does that feeling – ah! and i come one last time just a little bit, a tiny little shake, a little stutter, and all I can do is lay there on my side and breathe and I close my eyes and fall asleep and as I do I feel them lay down next to me, their poor spent cocks already shriveling, leaving little sticky wet trails over my thighs, and they put their arms around me and I can hear Mettaton’s voice like a throb in the back of my throat, laughing about something, telling my boyfriend something, and I’m so warm and tight and contained and I could stay there for ever and ever amen.

 

▪ ▪ ▪

 

When you come in you find Undyne curled up naked, still asleep. You guess what she’s been up to thanks to the lingering smell, not unpleasant, just strong, of her cum all over the sheets, dried by now. You take them off the bed, slowly so as not to wake her, get the spares out of the closet, cover her up. As you turn to go she grabs your hand and you see her eyes, narrow slits fixed on you. She pulls the sheet down, revealing a wide drowsy smile and she pulls you in, kisses you. “Don’t go,” she says, arms tight around your waist, and you get into bed, let her hold you, let her run her hips against yours, naked and unrestrained, and as her breathing regularizes again and she slips back into slumber you allow yourself a small smug smile.

**Author's Note:**

> Eh, this one's okay. I didn't really have a good grasp of how Undyne and Mettaton should interact and I still don't - I think in retrospect I should have used a different character, but the request was specifically for Mettaton so it is what it is. I think it's pretty hot though so it does have that going for it.


End file.
